fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/components/application-loader/loading-screen/loading-screen.tsx

@@ -0,0 +1,36 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { ReactElement } from 'react'
+import React from 'react'
+import { Alert } from 'react-bootstrap'
+import { LoadingAnimation } from './loading-animation'
+import { ShowIf } from '../../common/show-if/show-if'
+import styles from '../application-loader.module.scss'
+
+export interface LoadingScreenProps {
+  errorMessage?: string | ReactElement
+}
+
+/**
+ * Renders a loading animation.
+ *
+ * @param failedTaskName Should be set if a task failed to load. The name will be shown on screen.
+ */
+export const LoadingScreen: React.FC<LoadingScreenProps> = ({ errorMessage }) => {
+  return (
+    <div className={`${styles.loader} ${styles.middle} text-light overflow-hidden`}>
+      <div className='mb-3 text-light'>
+        <span className={`d-block`}>
+          <LoadingAnimation error={!!errorMessage} />
+        </span>
+      </div>
+      <ShowIf condition={!!errorMessage}>
+        <Alert variant={'danger'}>{errorMessage}</Alert>
+      </ShowIf>
+    </div>
+  )
+}